As stated by the former head of USGA.
It's basically a loophole in the rules that does not really benefit a player- if he was +2 in the event he wouldn't have gone near the ball because of fear of DQ.

The way he put it is.
If the same situation happens on the 12th at Augusta and the balls going into the creek, player races down and swats it back to the hole. He gets it to a foot and makes that putt.
Alternative is. Ball in the water, drop back over the creek and who knows what happens from there, he could fat on into the drink again like speith did.
He has willingly interfered with his ball because he didn't want to play it from where it was going to lie.

If he was +2 it would be more about the penalty strokes rather than fear of DQ for why he wouldn't do it.

Also, thats not the only alternative to the ball going in the water. You always have the option to drop the ball where you played the shot from and try again, which is always going to be a better option than playing a moving ball.